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The ecological consequences of biodiversity loss Michel Loreau Department of Biology, McGill University, Montreal E-mail: [email protected] Heading for a global biodiversity crisis Why does biodiversity matter? Biodiversity, ecosystem services, and human well-being Importance of “vertical” diversity Removal of sea otters Sea otter Population explosion of sea urchins Overgrazing of kelp Sea urchin Kelp • Extinction of other species living in kelp • Increased wave action, coastal erosion and storm damage • Evolution of chemical defences in kelp But what is the ecological significance of “horizontal” diversity? Neutral theory Functional redundancy Diversity Niche theory Functional complementarity Diversity Cedar Creek biodiversity experiment BIODEPTH biodiversity experiment Aboveground biomass (g/m2) Species diversity increases plant biomass production in grasslands Species richness Hector et al., Science 286: 1123–1127 (1999) Tilman et al., Science 294: 843–845 (2001) A general form of biodiversity– ecosystem functioning relationships? Cardinale et al., Nature 443: 989–992 (2006) Biodiversity effects on plant biomass production in BIODEPTH Selection effect (g1/2/m) Species richness Complementarity effect (g1/2/m) Species richness Loreau & Hector, Nature 412: 72–76 (2001) Biodiversity effects on plant biomass production: A meta-analysis Selection effect (g/m2) Complementarity effect (g/m2) Cardinale et al., PNAS 104: 18123–18128 (2007) The results of biodiversity experiments support niche theory Neutral theory Functional redundancy Diversity No net biodiversity effect No complementarity effect No selection effect Niche theory Functional complementarity Diversity Positive net biodiversity effect Positive complementarity effect Variable selection effect Biodiversity as insurance against environmental changes Yachi & Loreau, PNAS 96: 1463–1468 (1999) Biodiversity as insurance: Experimental evidence in grasslands and aquatic food webs Based on Tilman et al., Nature 441: 629–632 (2006) Steiner et al., Ecol. Lett. 8: 819–828 (2005) Biodiversity as insurance: Mechanisms 1. Asynchrony of species environmental responses (= temporal complementarity) 2. Overyielding (= functional complementarity) Biodiversity as insurance: Mechanisms in the Cedar Creek experiment Log CV of total biomass r2 = 0.27 (P < 10−9) r2 = 0.44 (P < 10−15) Log Synchrony of environmental responses Log Total biomass de Mazancourt et al., unpublished results Complex BEF relationships in food webs lC1mC1C1 C1 cH1C1H1C1 lH1mH1H1 cH1CSH1CS H1 mP1P1 cP1HSP1HS Plant P1 Carnivore CS cHSC1HSC1 … mH1H1 Herbivore cP1H1P1H1 lP1mP1P1 … mC1C1 Carnivore … HS L1 I lHSmHSHS PS mPSPS lPSmPSPS cLSPSLSPS Inorganic nutrient depletion zone ks1R mHSHS cPSHSPSHS Plant cL1P1L1P1 lCSmCSCS cHSCSHSCS Herbivore cPSH1PSH1 mCSCS … Inorganic nutrient depletion zone LS ksSR kL1 Inorganic nutrient pool kLS qR R Based on Thébault & Loreau, PNAS 100: 14949–14954 (2003) Complex BEF relationships in food webs H1 … HS−1 HS H1 … HS−1 HS P1 … PS−1 PS P1 … PS−1 PS Total biomass Both plant diversity and herbivore diversity vary Herbivores Herbivore diversity alone varies Plants Species richness Based on Thébault & Loreau, PNAS 100: 14949–14954 (2003) Biodiversity and ecosystem multifunctionality Hector & Bagchi, Nature 448: 188–190 (2007) Conclusions • Biodiversity loss does have significant impacts on ecosystem functioning and stability, and hence on ecosystem services, in particular: Horizontal diversity enhances resource use and biomass production through functional complementarity between species Horizontal diversity stabilises ecosystem properties through a combination of temporal and functional complementarity between species Conclusions • Trophic (and non-trophic) species interactions make biodiversity effects more complex; they are potentially a major source of surprises and uncertainty • The ecological consequences of biodiversity loss are still underestimated because recent work has focused on small scales and single ecosystem processes • There is now strong, rigorous scientific evidence that the loss of biodiversity and associated ecosystem services may be a serious threat to human well-being Thank you !
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